Electronic controls of a plutonium extraction battery employing neutron detectors



July 8, 1969 DEGRYSE ET AL 3,454,366

ELECTRONIC CONTROLS OF A PLUTONIUM EXTRACTION BATTERY EMPLOYING NEUTRON DETECTORS Filed June 21, 1966 A+L 5 Wp H abcae/ 9b/ k/ L United States Patent 3,454,366 ELECTRONIC CONTROLS OF A PLUTONIUM EXTRACTION BATTERY EMPLOYING NEU- TRON DETECTORS Michel Degryse, Morsang-sur-Orge, and Rene Riolfo, Bagnols-sur-Ceze, France, assignors to Commissariat a lEnergie Atomique, Paris, France Filed June 21, 1966, Ser. No. 559,251 Claims priority, application France, June 29, 1965,

Int. Cl. B01d 11/02 US. Cl. 23--270.5 7 Claims The present invention relates to a method for the electronic regulation of a plutonium extraction battery, and also to the regulating chain for carrying out said method.

The extraction batteries which it is here contemplated to regulate are of a known type and consist in a series of cans, each of which comprises a mixer and an decanting vessel, and through which are caused to flow in opposite directions, on the one hand, an aqueous solution containing uranium, plutonium and fission products, and, on the other hand, a solvent (e.g. tributylphosphate) used for extracting plutonium and uranium, the fission products being carried away by the exhausted aqueous phase.

The solvent phase is introduced into the extraction battery through an end can hereafter referred to, for clearness sake, as the upstream can; the aqueous solution is introduced through one of the downstream cans.

On the reverse, the battery delivers through the upstream can, an exhausted aqueous solution containing a very small amount of plutonium and uranium, on the one hand, and, through the most downstream can, the solvent containing substantially all the plutonium and the uranium, on the other hand.

In the extraction devices of the prior art, the thus recovered solvent still contains a small amount of fission products (about V and it is therefore necessary to carry out a second purification step.

The present invention aims at achieving a nearly total purification in a single step, which gives the extraction battery a maximum efficiency: the solvent introduced through the upstream can will provide, in the following preferential order, the extraction of uranium, then of plutonium and finally of the fission products. It can be admitted, according to a rough estimate, that when this solvent is saturated with uranium and plutonium, nearly the whole amount of fission products is carried away by the exhausted aqueous phase, and therefore that there will be a very small amount of these products left in the solvent.

This very small amount of fission products is made still smaller by another dissolution thereof in a washing aqueous phase introduced through the downstream can.

The decontamination coefiicient is thus substantially improved, as regards the fission products.

In order that the solvent be permanently loaded in spite of the variations of the parameters which define its saturation, it is necessary to keep a supply of extractable substance (uranium and plutonium) in the cans located upstream of the can through which the aqueous phase is introduced into the battery. Accordingly, the operator is compelled to alter the adjustment of the 8/11 ratio, viz. the ratio of the solvent flow-rate to the aqueous solution flow-rate, and to rely on the measurement of the plutonium retention provided by the counting of neutrons.

The requirements of the adjustment are such that the range of variation of said retention is very broad; hence, the regulation of the correction is of special interest.

Such a regulation has the advtange of considerably ice shortening the transient periods, the check analyses need not be so numerous and the operator is relieved of a rather critical task.

The general problem to be solved for obtaining the maximum efficiency of the extraction battery is to keep the solvent saturated with uranium and plutonium and free of fission products, while avoiding any substantial plutonium losses in the exhausted aqueous phase.

It is specially difiicult to meet such requirements, in view of the unstable chemical phenomena with occur in the battery, in particular in the intermediate cans, which con stitute a specially disturbed portion of the battery.

According to the prior art, it is first proceeded with the measurement of the uranium and plutonium solvent saturation, by applying either a discontinuous process (consisting in taking samples in the battery cans and testing said samples at the laboratory), or a continuous process, by detecting the neutrons resulting from the spontaneous fission of plutonium and the neutrons resulting from (a,n)-reactions on the light nuclei of the solvent and of the aqueous phase; then, the S/A ratio is caused to vary as a function of the thus measured solution condition, such an adjustment of the S/A ratio being carried out manually and at rest (by modifying the volume of the buckets of the dosing wheels which feed the battery with aqueous solution and solvent), which is a rather critical operation.

The method according to the invention substantially simplifies the methods of the prior art, in improving the continuous measurement of the solvent saturation by counting the neutrons, on the one hand, and in providing an automatic adjustment of the S/A ratio, on the other hand, said adjustment making use of the information provided by said continuous measurement.

More precisely, the present invention relates to a method for the electronic regulation of a plutonium extraction battery consisting in a series of cans, each of which comprises a mixer and a decanting vessel, and in which are caused to flow in opposite directions an aqueous solution containing uranium, plutonium and fission products, on the one hand, and, a solvent used for extracting said fission products with a view to purifying said plutonium and uranium, on the other hand, both liquid phases being introduced into the battery by means of rotating dosing means, said method being characterized in that it consists in associating to each of the cans of the disturbed portion of the extraction battery (viz. to each of the intermediate cans), a neutron detector, theory and practice both showing that the sum of the counting rates of said detectors substantialy varies as the plutonium retention in the battery, in adding the impulses delivered by said detectors and in integrating them, such an integration providing a measuring voltage which varies directly as said sum of the counting rates and, therefore, varies directly as the plutonium retention of the battery, in feeding a motor with a voltage which is the dilference between said measuring voltage and a set voltage, the speed of rotation of said motor being proportional to said difference, and in adjusting the ratio of the solvent flow-rate to the aqeuous solution flow-rate of said rotating dosing means in proportion to the speed of rotation of said motor, whereby said ratio will vary directly as the diflerence between the measured value of the plutonium retention of the battery and a set value.

The solvent used for xetracting the fission products is tributylphosphate, for instance.

The present invention also relates to an electronic regulating chain for carrying out the above method, said regulating chain being characterized in that it comprises a series of neutron detectors, each of which is associated to one of the cans of the battery disturbed portion (viz.

the intermediate cans), an adding circuit adapted to add the impulses delivered by said detectors, an integrator having a high time constant and actuated by said adding circuit, said integrator being adapted to deliver a mesuring voltage which varies directly as the sum of the counting rates of said detectors and, therefore, directly as the plutonium retention in the intermediate cans, an amplifier adapted to amplify the difference between said measuring voltage and a set voltage, a motor fed by said voltage difference and the rotation speed of which varies directly as said voltage difierence, and a mechanical device adapted to be driven by said motor and to adjust the ratio of the solvent flow rate to the aqueous solution flow-rate of said rotating dosing means, in direct proportion to the speed of rotation of said motor.

Said rotating dosing means can be dosing wheels, for instance and said neutron detectors are, for instance, counting-detectors containing boron trifluoride.

According to a convenient embodiment, one of said rotating dosing means has a constant speed of rotation, and said mechanical device comprises a mechanical differential actuated by said motor and adapted to adjust, in direct proportion to the speed of rotation of the latter, the difference between the speeds of rotation of the dosing means and therefore, since one of these speeds has a constant value, the ratio of the solvent flow-rate to the aqueous solution flow-rate of said rotating dosing means.

The features of the present invention will be disclosed hereafter, reference being made to the accompanying sole figure, which is a diagram of the regulatingchain according to the invention.

The extracting battery B is constituted by can P and cans a, b, c 1; In, each of said cans comprising a mixer and a decanting vessel.

The average plutonium and uranium concentrations of the aqueous phase A are (Pu) =10 g./l. and (U) =80 g./l., respectively; said aqueous phase, which contains fission products (F P) is introduced into battery B through can i. The washing aqueous phase L, which is introduced into the battery through can m, improves the decontamination coefficient as regards fission products (-FP). Through can P are evacuated the aqueous phases A and L which contain said fission products.

Clean solvent S (tributylphosphate, for instance) is introduced through can P and leaves battery B thorugh can m, said solvent being then loaded with plutonium and uranium, the concentration of which are (Pu) and (U) respectively.

A series of six detectors 1 are located in the vicinity of the decanting vessels of the intermediate cans c, d, e, f, g and h of the extracting battery B. Said detectors are for instance counting detectors containing BF (boron trifluoride) and comprising a cylindrical copper cathode and a coaxial anode, the BE, contained therein being enriched with B which increases sensitivity.

The impulses provided by said six detectors are amplified in pre-amplifiers 2, then they go through an amplifier, a discriminator and a setting circuit forming, for instance, a transistorised discrimination unit 3, and they are finally directed to an input circuit 4.

Said input circuit 4 comprises an OR circuit, which adds the impulses delivered by the six different ways and a test circuit which generates 50 to 25 Hz. impulses and permits to check the operation and the adjustment of integrators 5 and 6.

Integrator 5 delivers a voltage (0, v.) which is directly proportional to the counting rate of the detector of can 0; its time constant is 500s and the counting rate are 3, 10 and 30 shocks per second, in order to fit the apparatus to the sensitivity of the measurements.

Said integrator serves as an alarm device, adapted to Warn of any excessive plutonium leakage in the exhausted aqueous phase in can P. The voltage delivered :y said integrator is displayed on an alarm voltmeter 7;

whenever said voltage goes beyond the value displayed, it controls a sighting board 8.

Integrator 6 delivers a voltage (0, +10 v.) which is directly proportional to the sum of the six detectors counting-rates and, therefore, directly proportional to the plutonium retention in cans c to h; its time constant is 500s and the counting rates are 20, 60, and 200 shocks per second.

The voltage delivered thereby is displayed on a regulating voltmeter 9 and on a six-way potentiometric recorder 1'0, provided with a scalewhich is graduated as that of voltmeter 9. Said voltage is compared to a set-voltage displayed at 11, at the input of power-amplifier 12. The set-voltage is displayed on a voltmeter 13 graduated as regulating-voltmeter 9.

The difference between the measuring-voltage and the set-voltage is amplified in amplifier 12 and controls a two-phase motor 14 having a power of 5 W.

The alternating voltage delivered by the tachometric generator 21 is injected into power amplifier 12 and into the demodulating device and the differential amplifier 11 and 15, which deliver a direct voltage which is directly proportional to the speed of rotation of motor 14, and the algebraic sign of which is indicative of the direction of rotation. This voltage is displayed on potentiometric recorder 10, which bears a scale graduated in terms of the solvent flow-rate variations in percent (maximum of :30%

The two-phase motor 14 controls a speed-reducer 20, the reducing ratios of which are .75/ 20, l/20 and 1.25/ 20. These three ratios permit to scan the whole range of the aqueous flow-rates (A and L) delivered by the dosing wheels 16 and 17. The output shaft of speed-reducer 20 controls the outer crown of diflerential 18.

The rotation speeds vary according to the following equation:

B B m with R=.75, 1 or 1.25, m being the rotation speed of dosing wheels 16 and 17 m the speed of rotation of Wheel 19 for dosing solvent S, and m the speed of rotation of motor 14.

It results from the above that the regulating chain according to the invention causes the S/A ratio (viz. the ratio of the solvent flow-rate to the aqueous solution flow-rate), to vary in direct proportion to the difference between the measured retention value and the set-value.

A potentiometer located on the displaying device 11 permits to adjust the gain of the regulating chain. Moreover, a switch and a manual display-potentiometer mounted on said displaying device 11 permit to control two-phase motor 14 by hand.

For safety sake, it is advisable that each of the elements of the regulating chain be duplicated.

The following comparative table is indicative of some favorable results obtained with the method according to the present invention:

Present Prior Art application 7 Activity Decontamination factor (DF) of plutonium, as regards fission products (FF).

What is claimed is:

1. An electronic regulating chain for the electronic regulation of solution and solvent introduction into a plutonium extraction battery consisting of a series of cans, each of which comprises a mixer and a decanting vessel, and in which are caused to fiow, in opposite directions, an aqueous solution containing uranium, plutonium and fission products introduced into one end of said battery through a solution inlet conduit, and a solvent used for extracting said fission products introduced at the opposite end of said battery through a solvent inlet conduit to purify said plutonium and uranium, the introduction of both said liquid "phases into the battery being controlled by rotating dosing means in said inlet conduits, said controlling means comprising a series of neutron detectors, one of which is associated with the decanting vessel of each of the intermediate cans in the extraction battery, an adding circuit adapted to add the impulses delivered by said detectors, an integrator having a high timeconstant and actuated by said adding circuit, said integrator being adapted to deliver a measuring voltage which varies directly as the sum of the counting rates of said detectors and is directly proportional to the plutonium retention in the intermediate cans, means to receive said measuring voltage from said integrator and to compare the measuring voltage with a set voltage, an amplifier means to amplify the difference between said measuring voltage and said set voltage, a motor fed by said voltage difference, and the rotation speed of which varies directly as said voltage difference and a mechanical dilferential to be driven by said motor and to adjust the ratio of the solvent flow-rate to the aqueous solution flow-rate of said rotating dosing means in direct proportion to the speed of rotation of said motor.

2. An electronic regulating chain according to claim 1 wherein the rotating dosing means are dosing wheels.

3. An electronic regulating chain according to claim 1, wherein the neutron detectors are counting detectors containing boron trifluoride.

4. A regulating electronic chain according to claim 3, wherein said counting detectors comprise a copper cylindrical cathode and a coaxial anode filled with boron trifluoride enriched with B 5. An electronic regulating chain according to claim 1, wherein one of the rotating dosing means has a constant rotating speed and said mechanical device comprises a mechanical differential actuated by said motor and adapted to adjust, in direct proportion to the speed of rotation of the motor, the difference between the speeds of rotation of the dosing means and therefore, the ratio of the solvent flow-rate to the aqueous solution flow-rate of said rotating dosing means.

6. An electronic regulating chain according to claim 1, wherein a pre-amplifier, an amplifier, a discriminator and a setting means are connected between each of the neutron detectors and the adding circuit.

7. An electronic regulating chain according to claim 1, wherein a second integrator having a high time-constant is directly and solely actuated by the impulses delivered by the detector corresponding to the can which is adjacent the solvent inlet conduit end of the intermediate cans, said second integrator acting as an alarm.

1:. References Cited UNITED STATES PATENTS 2,882,124 4/1959 Seaborg 23-312 X 2,893,822 7/1959 Hyman 23-312 X 2,893,824 7/1959 Hyman 23312 X 3,050,624 8/ 1962 Janner 250-831 3,141,092 7/1964 Weinberg 250-831 X 3,225,200 12/1965 Gey 25083.l 3,332,744 7/1967 Henderson 23267 X 3,381,131 4/1968 Meal 25083.1

FOREIGN PATENTS 960,548 6/ 1964 Great 'Britain.

1,031,194 6/1966 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

S. I. EMERY, Assistant Examiner.

US. Cl. X.R. 

1. AN ELECTRONIC REGULATING CHAIN FOR THE ELECTRONIC REGULATION OF SOLUTION AND SOLVENT INTRODUCTION INTO A PLUTONIUM EXTRACTION BATTERY CONSISTNG OF A SERIES OF CANS, EACH OF WHICH COMPRISES A MIXER AND A DECANTING VESSEL, AND IN WHICH ARE CAUSED TO FLOW, IN OPPOSITE DIRECTIONS, AN AQUEOUS SOLUTION CONTAINING URANIUM, PLUTONIUM AND FISSION PRODUCTS INTRODUCED INTO ONE END OF SAID BATTERY THROUGH A SOLUTION INLET CONDUIT, AND A SOLVENT USED FOR EXTRACTING SAID FISSION PRODUCTS INTRODUCED AT THE OPPOSITE END OF SAID BATTERY THROUGH A SOLVENT INLET CONDUIT TO PURIFY SAID PLUTONIUM AND URANIUM, THE INTRODUCTION OF BOTH SAID LIQUID PHASES INTO THE BATTERY BEIN CONTROLLED BY ROTATING DOSING MEANS IN SAID INLET CONDUITS, SAID CONTROLLING MEANS COMPRISING A SERIES OF NEUTRON DETECTORS, ONE OF WHICH IS ASSOCIATED WITH THE DECANTING VESSEL OF EACH OF THE INTERMEDIATE CANS IN THE EXTRACTION BATTERY, AN ADDING CIRCUIT ADAPTED TO ADD THE IMPULSES DELIVERED BY SAID DETECTORS, AN INTEGRATOR HAVING A HIGH TIMECONSTANT AND ACTUATED BY SAID ADDING CIRCUIT, SAID INTEGRATOR BEING ADAPTED TO DELIVER A MEASURING VOLTAGE WHICH VARIES DIRECTLY AS THE SUM OF THE COUNTING RATES OF SAID DETECTORS AND IS DIRECTLY PROPORTIONAL TO THE PLUTONIUM RETENTION IN THE INTERMEDIATE CANS, MEANS TO RECEIVE SAID MEASURING VOLTAGE FROM SAID INTEGRATOR AND TO COMPARE THE MEASURING VOLTAGE WITH A SET VOLTAGE, AN AMPLIFIER MEANS TO AMPLIFY THE DIFFERENCE BETWEEN SAID MEASURING VOLTAGE AND SAID SET VOLTAGE, A MOTOR FED BY SAID VOLTAGE DIFFERENCE, AND THE ROTATION SPEED OF WHICH VARIES DIRECTLY AS SAID VOLTAGE DIFFERENCE AND A MECHANICAL DIFFERENTIAL TO BE DRIVEN BY SAID MOTOR AND TO ADJUST THE RATIO OF THE SOLVENT FLOW-RATE TO THE AQUEOUS SOLUTION FLOW-RATE OF SAID ROTATING DOSING MEANS IN DIRECT PROPORTION TO THE SPEED OF ROTATIN OF SAID MOTOR. 